I have a stock 351w in my 88f250. First thing I was going to do is get a set of headers and exaust pipes. They whould have to be small tube headers cuz the ports are really small. I was wondering what size exaust pipe would be best. My friend suggested 3 inch, as thats what he got for his. But another guy told me 3 inch is too big that it would be a waste. Would it be a waste if I bought new heads with larger ports and larger tubed manifolds?

 

I have a 93 F150 302 with a 3''MagnaFlow that I love. It was 2.5'' and went 3'' cat-back. didn't have much choice since the muffler was free. It sure helped.

 

You say going to 3" really helped. Can you quantify this for me? I have what I believe to be stock replacement exhaust, cat, and muffler (single exhaust out) on my 1990 F250 351w. Would changing to headers and 3" exhaust give me any more power? Can you quantify this for me or point me to a link that can reduce "feel" to actual numbers?

 

Nope, don't have any specific data on if a 3'' is better than a 2 1/2'' I just know that changing my stock 2 1/2'' muffler that had holes in it to a 3'' MagnaFlow really helped. I will e-mail my friend and MagnaFlow who is near owning MagnaFlow(how I got it for free) and ask him if he has data on it. I doubt if there is much difference in performance than there is difference is sound. 3'' resonates more. I would say chaning the header and exhaust would give you a lot more power, I wouldn't know how much though....Hope this helps....

 

I think the stock manifolds are what really kills the power.

 

Exh port size is not a big issue, although I wouldn't go larger than 1 5/8" primaries on a stock motor. If you go dual, then 2 1/4" will be fine. If you do a single, there is nothing wrong with 3". The power gains are worthwhile and useable throughout the rpm range.
I have Hedman 1 5/8ths into custom 2 1/4'ers into the factory cat (empty) exiting into a 3" aluminized pipe to the rear axle, with a bullet muffler, turned down.